Flashback shut-off

ABSTRACT

A flashback-arresting shut-off valve is disclosed herein. Propellant is moved from a propellant reservoir, through the shut-off valve in an open configuration to a point of combustion in a normal propellant flow direction. During a flashback, the propellant is ignited within the propellant line and substantial physical/thermal energy caused by the flashback travels in the direction opposite to the normal propellant flow direction back to the shut-off valve. A burst member within the shut-off valve fails because of the flashback. Failure of the burst member causes compression on a spring-loaded portion of the shut-off valve to be released, thereby closing the shut-off valve and sealing the propellant reservoir from the flashback. Failure of the burst member also causes one or more pressure relief outlets to open that direct the physical/thermal energy and/or un-combusted/combusted propellant out and away from the shut-off valve.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims benefit of priority to U.S. Provisional Patent Application No. 61/223,611, entitled “Propulsion Systems and Components Thereof” and filed on Jul. 7, 2009, which is specifically incorporated by reference herein for all that it discloses or teaches. Further, the present application is related to U.S. patent application Ser. No. 11/950,174, entitled “Spark-Integrated Propellant Injector Head With Flashback Barrier,” filed on Dec. 4, 2007; and to U.S. patent application Ser. No. 12/633,770 entitled “Regeneratively Cooled Porous Media Jacket,” filed on Dec. 8, 2009. Still further, the present application is related to U.S. patent application Ser. No. ______, entitled “Tiered Porosity Flashback Suppressing Elements For Monopropellant Or Pre-Mixed Bipropellant Systems” (Attorney Docket No. 488-011-USP1); U.S. patent application Ser. No. 12/831,703, entitled “Detonation Wave Arrestor” (Attorney Docket No. 488-011-USP2); and U.S. patent application Ser. No. ______, entitled “Aluminum Porous Media” (Attorney Docket No. 488-011-USP4); all three of which are filed on Jul. 7, 2010, and which are also specifically incorporated by reference herein for all they disclose or teach.

BACKGROUND

Power generation systems (e.g., propulsion systems, working fluid production systems, and electricity generation systems) often utilize a finite stored fuel source (e.g., a fuel tank) to provide fuel to the power generation system. Some power generation systems also utilize a stored oxidizer source (e.g., an oxidizer tank). These systems are known as bipropellant systems. For example, bipropellants are commonly used in liquid-propellant thrusters on orbital vehicles. Other power generation systems utilize ambient air as an oxidizer rather than a stored oxidizer source (e.g., typical internal combustion engines and turbofan/jet aircraft engines).

In bipropellant systems, so long as the fuel source and oxidizer are separated, neither are flammable in systems not exposed to the atmosphere. For example, fuel sealed within a fuel line or fuel leaking into a vacuum is not flammable). Similarly, in systems utilizing ambient air as an oxidizer, the fuel source is not flammable until exposed to the ambient air (e.g., at a fuel injector in an automobile).

This feature in bipropellant and ambient air propellant systems serves a safety function because a flame existing at the point of ignition cannot travel up fuel and/or oxidizer lines past the point the fuel and oxidizer are mixed together. This prevents the flame from traveling back to the fuel tank in the bipropellant and ambient air propellant systems and causing an explosion. As a result, the fuel and oxidizer in many bipropellant and ambient air propellant systems are not mixed until at the point of ignition (e.g., within a combustion chamber in a jet engine or within a cylinder in an internal combustion engine).

In bipropellant thrusters on orbital vehicles, it is often desirable to store exact quantities of finite stored fuel source and oxidizer source so that they are exhausted simultaneously during combustion. Any fuel or oxidizer left after its counterpart is exhausted is wasted. Further, leftover fuel or oxidizer creates excess weight and volume during the travel of the orbital vehicle. Considerable time and effort is spent calculating the appropriate quantities of fuel and oxidizer to store on an orbital vehicle, measuring consumption of the fuel and oxidizer, and detecting when the fuel and oxidizer are spent. It is desirable to avoid these calculation, measurement, and detection functions on an orbital vehicle while it is in flight.

Still other power generation systems utilize a stored monopropellant source. A monopropellant is a single energetic fluid (i.e., a liquid, gas, or combination thereof, sometimes with solid particles entrained within the liquid or gas) that decomposes to liberate gases and heat. This heated gas can drive other applications (e.g., thrusters, power systems, inflation bags, etc.). Monopropellants typically include either a single chemical or a mixture of multiple chemicals that when combined produce a monopropellant blend. In the monopropellant blend, the constituent chemicals most commonly remain well mixed and effectively behave as a single energetic fluid. Many bipropellants (e.g., a combination of a fuel and an oxidizer such as vaporized fuel and air) when mixed together effectively act as a monopropellant. Monopropellants can provide a simpler and more reliable feed-system implementation for spacecraft due to the fewer number of fluids that need to be precisely managed.

In one example implementation, the monopropellant is stored as a liquid and decomposes into a hot gas in the presence of an appropriate catalyst, upon introduction of a high-energy spark, or upon introduction of a similar point source ignition mechanism. Example monopropellants include hydrazine, which is often used in spacecraft attitude control jets and hydroxyl ammonium nitrate (HAN). Given the combustible nature of a monopropellant, in an unintentional line ignition of the monopropellant, the monopropellant can act like a fuse and generate combustion waves that can move very rapidly through a fluid conduit or path full of monopropellant (i.e., a flashback). Monopropellants and supply systems for thrusters and other work producing systems are subject to damage when the combustion waves progress upstream from a combustion chamber to and through monopropellant supply lines. The danger of flashback from the point of ignition of the monopropellant (or other point along the monopropellant feed line) back to a monopropellant storage tank has prevented the widespread utilization of monopropellants. As a result, flashback arrestors are needed to prevent flashbacks from reaching the monopropellant storage tank and causing an explosion.

Flashback arrestors are known as safety devices in systems where a combustible mixture may be within pipes, tubes, or other flow paths (e.g., in oxygen-actylene welding equipment and flammable gas vents). However, these existing flashback arrestors are insufficiently robust to provide adequate protection to monopropellant storage and feed systems due to the high pressure and energy content of monopropellants used for power generation systems.

SUMMARY

Implementations described and claimed herein address the foregoing problems by providing a propellant shut-off assembly for isolating a propellant source in the event of a flashback. The propellant shut-off assembly may include a burst membrane configured to fail in presence of the flashback and a biased closed shut-off valve attached to the burst membrane. The shut-off valve is held open by the burst membrane while the burst member is intact.

In another implementation, the foregoing problems are addressed by a method of isolating a propellant source in the event a flashback. While propellant moves through the propellant shut-off assembly in a propellant flow direction, the propellant shut-off assembly may experience a flashback. As a result, a burst membrane within the propellant shut-off assembly is fractured to failure as a result of the flashback. Failure of the burst membrane causes the propellant shut-off assembly to close and isolate a propellant source from any components of the propellant delivery system that have failed as a result of the flashback.

Yet another implementation provides a propellant delivery system including a propellant reservoir and a propellant shut-off assembly. The propellant shut-off assembly may include a burst membrane configured to fail in presence of the flashback and a biased closed shut-off valve attached to the burst membrane. The shut-off valve is held open by the burst membrane while the burst member is intact. The propellant delivery system further includes a propellant injector. The flashback originates between the propellant injector and the propellant shut-off assembly and the propellant shut-off assembly isolates the propellant reservoir from any components of the propellant delivery system that have failed as a result of the flashback.

Other implementations are also described and recited herein.

BRIEF DESCRIPTIONS OF THE DRAWINGS

FIG. 1A is a perspective schematic view of an orbital or spacecraft with several attitude or apogee thrusters using the presently disclosed flashback-arresting devices.

FIG. 1B is an enlarged schematic cross section of an example monopropellant propulsion system in the orbital vehicle using flashback-arresting devices according to the presently disclosed technology.

FIG. 2 illustrates an example flowchart for monopropellant and bipropellant systems using flashback-arresting devices for flashback protection in propulsion systems, working fluid production systems, and/or electricity generation systems.

FIG. 3 illustrates a cross-sectional view of an example closed flashback deflector and shut-off valve assembly.

FIG. 4 illustrates a three-quarter sectional view of an example closed flashback deflector and shut-off valve assembly.

FIG. 5 illustrates a cross-sectional view of an example open flashback-arresting deflector and shut-off valve assembly, showing propellant flowing through the assembly.

FIG. 6 illustrates a cross-sectional view of an example closed flashback-arresting deflector and shut-off valve assembly, showing a flashback diverted out of the assembly.

FIG. 7 illustrates example operations for arresting a flashback using a flashback-arresting shut-off valve according to the presently disclosed technology.

DETAILED DESCRIPTIONS

Chemically reacting monopropellants and mixed fuel/oxidizer blends contain constituents that liberate energy through thermal decomposition and/or combustion. In combustion reactions, the reactants are at a higher energy state than the products remaining following combustion of the reactants. However, a certain quantity of energy (i.e., activation energy) is input to release the energy stored within the chemical bonds of the reactants.

This chemical energy release is often initiated by an ignition source, which provides the activation energy for a selected monopropellant or fuel/oxidizer blend. The ignition source is typically incorporated near an injector head and within a combustion chamber of a power generation system. Many ignition sources exist including, but not limited to, electrical sparks, catalysts (i.e., substances which lower the activation energy by providing a surface which increases a reaction's chemical kinetics), heat sources, impact loads, compression, or any combination thereof.

If the ignition source is oriented downstream (i.e., in a direction away from the fluid energy storage device) of a monopropellant or a mixture of fuel(s) and oxidizer(s), flames at the ignition source can propagate upstream (i.e., in a direction towards fluid energy storage) through the feed lines to the point where the fuel(s) and oxidizer(s) are mixed or into a monopropellant storage tank. This event, commonly referred to as a flashback, may cause catastrophic system failure (e.g., destruction of the power generation system, destruction of surrounding equipment, and/or injury or death to nearby personnel).

Flashbacks may take the form of deflagration or detonation wave propagation. Deflagration is a common form of combustion where a flame speed travels at sub-sonic speeds. Deflagration combustion is commonly associated with relatively low energy content and chemical reaction rates. Detonation is a phenomenon characterized by supersonic flame front propagation. Pressure and temperature spikes as well as shock waves are typically associated with detonation waves. Detonation waves contain immense power, which can be very useful in a controlled environment or very destructive in an uncontrolled environment. Conventional flashback-arresting devices designed to prevent deflagration flashbacks are often not robust enough to survive detonation flashback waves. Flashback arrestors disclosed herein are specifically configured to effectively prevent and/or control detonation flashback waves as well as deflagration flashbacks.

FIG. 1A is a perspective schematic view of an orbital or spacecraft 100 with several attitude or apogee thrusters using the presently disclosed flashback-arresting devices. The thrusters 110 may use a monopropellant propulsion system 110 that is described below in further detail in FIG. 1B.

FIG. 1B illustrates a cross-sectional view of an example monopropellant propulsion system 110 using flashback-arresting devices 102, 104, 106 according to the presently disclosed technology. The example monopropellant propulsion system 110 includes a monopropellant tank 112. An ignition interface 106 is located between a thruster body 111 and a combustion chamber 114, which feeds into an expansion nozzle 116. In the illustration, the system 110 would be propelled from left to right.

Propellant from the monopropellant tank 112 is fed to the combustion chamber 114 via monopropellant lines (e.g., monopropellant line 118). Flashback-arresting shut-off valve 102 shuts off the monopropellant in the event of a flashback. Flashback-arresting deflector 104 diverts the energy caused by the flashback away from the monopropellant lines and tank 112. Flashback-arresting ignition interface 106 may contain a micro-fluidic porous media element of sintered metal or other heat resistance materials. Further, the shut-off valve 102 and/or deflector 104 may also contain one or more micro-fluidic porous media elements, as well. Note that while the flashback arresting devices 102, 104, 106 are disclosed in FIGS. 1A and 1B with respect to a orbital or spacecraft 100, such devices may also be used in other propellant and/or power generation systems.

The micro-fluidic porous media element, by virtue of multiple small and convoluted flow paths, allows monopropellant to flow through the media element but prevents a flashback from traveling back through the media element. Further, the media element may have a variable density design to provide desired flow characteristics. Still further, the media element may have various internal micro-channel designs as well as various external geometries (e.g., a disk, cup, or ring). The media element may also be constructed of various materials and have various coatings as described in detail with regard to FIG. 4.

FIG. 2 illustrates an example flowchart 200 for monopropellant and bipropellant systems using flashback-arresting devices for flashback protection in propulsion systems (e.g., thruster 220), working fluid production systems (e.g., gas generator 222), and/or electricity generation systems (e.g., power plant 224). In a first depicted implementation, monopropellant tank 226 is the fuel/oxidizer source for a power generation system 220, 222, or 224. Flashback valve 228, flashback deflector 230, and/or regulator 232 contain flashback-arresting technology as presently disclosed. The flashback-arresting technology prevents or stops a flashback from propagating upstream and causing catastrophic system failure in monopropellant feed lines and/or monopropellant tank 226. Further, the presently disclosed flashback-arresting technology (e.g., flashback deflector 230) may also divert energy of the flashback away from the feed lines and/or monopropellant tank 226.

In a second depicted implementation, bipropellant tanks (i.e., fuel tank 228 and oxidizer tank 230) are premixed before injection into the power generation system 220, 222, or 224. Example fuels for such systems include, without limitation, natural gas, gasoline, diesel, kerosene, ethane, ethylene, ethanol, methanol, methane, acetylene, and nitro methane. Example oxidizers for such systems include, without limitation, air, oxygen/inert gas mixtures, oxygen, nitrous oxide, and hydrogen peroxide. Fuel components can be mixed with oxidizing components in many different ratios to obtain a desired combustion reaction. While FIG. 1B illustrates a bipropellant configuration utilizing one fuel tank 228 and one oxidizer tank 230, it should be understood that the presently disclosed technology could be applied to bipropellant mixtures involving multiple fuel and/or oxidizer components as well as additional smaller trace components that may aid in the combustion process or provide desirable end results in the resultant gas plumes (e g, inhibition of undesirable trace gas species such as NOx formation, promotion of fuel/air combustion initiation, promotion of good fuel/air mixing, and/or alteration of fluid species with embedded solid particles).

Flashback valve 234, flashback deflector 236, and/or the regulator 232, contain flashback-arresting technology as presently disclosed. The flashback-arresting technology prevents or stops a flashback from propagating upstream and causing catastrophic system failure in feed lines downstream of where fuel is premixed with oxidizer. Further, the presently disclosed flashback-arresting technology (e.g., flashback deflector 236) may also divert energy of the flashback away from the feed lines and/or fuel tank 228 and oxidizer tank 230.

Further, FIG. 2 illustrates three alternative power generation systems (i.e., thruster 220, gas generator 222, and power plant 224), each with a corresponding injector head 238. Other power generation systems are also contemplated herein. For example, various work extracting cycles may implement the flashback-arresting technology (e.g., gas turbine (Brayton) cycles, Otto cycles, diesel cycles, constant pressure cycles). The injectors 234 may also be equipped with the aforementioned flashback-arresting technology that prevents or stops a flashback from propagating upstream of the injectors 234 and causing catastrophic system failure.

FIG. 3 illustrates a cross-sectional view of an example closed flashback deflector and shut-off valve assembly 300. The assembly 300 provides flashback (i.e., detonation and/or deflagration) protection to propellant (e.g., monopropellant and/or mixed fuel/oxidizer) sources upstream from the assembly 300. The assembly 300 includes a housing 318 with a top cap 304 and a bottom cap 316 rigidly attached to an upper end and a lower end of the assembly 300, respectively, along central axis 348. The top and bottom caps 304, 316 may be attached to the housing 318 using a variety of methods and/or structures (e.g., press-fitting, welding, gluing, bolting, and/or screwing). Some of the attachment methods/or structures are permanent (e.g., welding). Other attachment methods and/or structures enable the assembly 300 to be disassembled with relative ease for inspection, repair, and/or maintenance (e.g., bolting and screwing).

The housing 318, top cap 304, and bottom cap 316 form an enclosure for the flashback deflector 302 and shut-off valve components. At least propellant inlet tube 310, ball bearing 320, receptor 326, burst membrane 308, and compression springs collectively make-up the shut-off valve. The bottom cap 316 includes a central aperture 346 for receiving the propellant inlet tube 310.

The propellant tube 310 is fixedly attached to the bottom cap 316 and extends through the central aperture 346 to the receptor 326. The propellant tube 310 is slidably attached to the receptor 326 and the receptor 326 is adapted to move upward and downward along the central axis 348 while the propellant tube 310 remains fixed in place within the assembly 300. Bellows 328 is fixedly attached to the outside of the propellant tube 310 near the bottom of the assembly 300 and extends upward along the propellant tube 310 and is fixedly attached to the bottom of the receptor 326 where the receptor 326 meets the propellant tube 310. The bellows 328 is adapted to extend and retract with movement of the receptor 326 and create a hermetic seal for the slip-fit between the receptor 326 and the propellant tube 310.

The propellant tube 310 includes a seat 322 at the upper end of the propellant tube 310 along the central axis 348. Further, the receptor 326 includes an aperture 350 for receiving the ball bearing 320 or another structure adapted to seal against the seat 322 (e.g., a needle). The ball bearing 320 may be press-fit, welded, glued, or otherwise attached to the aperture 350. In another implementation, the ball bearing 320 is not attached to the aperture 350 and is free to move between the aperture 350 and seat 322 when the assembly 300 is open (see e.g., FIG. 5). In this implementation, the ball bearing 320 may act as a check valve, thereby preventing propellant flow from reversing by resting in the seat 322. In the closed position of the assembly 300, as shown in FIG. 3, the ball bearing 320 is compressively mated to the seat 322, thereby making a hermetic seal.

The receptor 326 includes threaded apertures (e.g., aperture 352) for receiving threaded rods (e.g., threaded rod 340) extending downwardly away from the receptor 326 through apertures (e.g., aperture 358) in the housing 318. In other implementations, the threaded apertures and threaded rods are not threaded and are instead press-fit, welded, glued, or otherwise fixedly attached to one another. The threaded rods extend through apertures (e.g., aperture 364) in a spring plate 354 and are secured to the spring plate 354 with nuts (e.g., nut 342). The spring plate 354 floats within the housing 318, attached only to one end of one or more springs (e.g., spring 324).

The springs encircle each threaded rod and extend from the receptor 326 to the spring plate 354. The springs are in compression, forcing the receptor 326 downward with relation to the fixed propellant inlet tube 310. As a result, the ball bearing 320 is compressively sealed against the seat 322 on the propellant tube inlet 310. Each of the springs may have any configuration with compressive spring force (e.g., one or more stacked spring washers, one or more stacked Belleville washers, one or more helicoidal springs, spring steel in compression, etc.). Other assemblies may have springs under tension rather than compression. Still other assemblies may not have springs; instead, they may have an electronic sensor and an electric actuator (solenoid) to compressively seal the ball bearing 320 against the seat 322. The springs and/or other mechanisms adapted to seal the ball bearing 320 against the seat 322 generate sufficient force to seal the propellant inlet tube 310 quickly and positively against the seat 322. The bottom cap 316 also includes apertures (e.g., aperture 344) for accessing the nuts (e.g., nut 342). During assembly and/or adjustment, rotation of the nuts adjusts the compressive force of the springs and/or position of the spring plate 354 and receptor 326 with respect to the housing 318 and propellant inlet tube 310.

The receptor 326 may also include a porous media element 330. When the assembly 300 is in an open configuration (see e.g., FIG. 5), the porous media element 330 provides a path for combustible fluid to flow from the propellant inlet tube 310 through the receptor 326. The effective microchannel diameter sizing and surface area of the porous media element 330 are strategically chosen for each particular application based on combustible fluid mass flow rate requirements and allowable pressure drop while maintaining a desired flashback protection.

The implementation of FIG. 3 depicts the assembly 300 in a closed position. The closed position is indicative of an incident causing flashback. The porous media element 330 operates as a thermal sponge that absorbs combustion energy at rates higher than the rate at which a detonation wave can release combustion energy. As a result, the porous media element 330 provides detonation quenching.

While the quenching distance of the porous media element 330 may be sufficient to arrest a primary detonation wave, the energy released from a flashback can cause secondary ignitions through mechanical failures and/or heat transport through solid material. This conductive heat transport can produce hot spots in direct contact with un-combusted combustible fluid sufficient to ignite a propellant upstream of the assembly 300.

In one implementation, a flashback deflector 302 is located above the receptor 326, downstream of the porous media element 330 to disperse the energy released from the flashback. Further, a burst membrane 308 is located around the flashback deflector 302. The flashback deflector 302 together with the burst membrane 308 provides additional protection to propellant lines and/or sources upstream from the assembly 300 from the potential harm caused by a flashback. Specifically, the flashback deflector 302 together with the burst membrane 308 allows flashback thermal/physical energy and/or combusted/un-combusted propellant to be vented out of the assembly 300 in the vicinity of the flashback deflector 302 (see FIG. 5 for details). Moreover, the flashback deflector 302, when hit by a detonation wave, disperses the detonation wave away from the porous media element 330. Specifically, the flashback deflector 302 directs the shock wave energy towards the burst membrane 308.

When the flashback energy reaches the burst membrane 308, the burst membrane 308 fractures and fails, allowing the flashback energy, including in some implementations combusted and/or un-combusted propellant, to continue out of the assembly 300 via one or more pressure relief outlets (e.g., shockwave outlet 314). Further, the compression of the springs overcomes any remaining portions of the burst membrane 308, forces the ball bearing 320 into the seat 322, and thus closes the assembly 300, as depicted in FIG. 3.

While the burst membrane 308 is intact, it resists the compressive force of the springs (e.g., spring 324), allowing the ball bearing 320 to remain away from the seat 322 and keeping the assembly 300 in an open configuration (see e.g., FIG. 5). The top cap 304 is positioned over the flashback deflector 302 and includes a propellant outlet aperture 312. In some implementations of the assembly 300, no flashback deflector 302 and/or porous media element 330 are present.

FIG. 4 illustrates a three-quarter sectional view of an example closed flashback-arresting deflector and shut-off valve assembly 400. The assembly 400 provides flashback (i.e., detonation and/or deflagration) protection to propellant (e.g., monopropellant and mixed bipropellant) lines and/or sources upstream from the assembly 400. The assembly 400 includes the same components of the assembly 300 of FIG. 3. In addition, the assembly 400 also includes propellant passage 460, which serves as a conduit for propellant flowing from the propellant inlet tube 410 to the receptor 426 (not shown in FIG. 3).

More specifically, the assembly 400 includes various high-strength components that normally are not exposed to propellant while the assembly 400 is in an open configuration (e.g., housing 418, top cap 404, bottom cap 416, springs, threaded rods, nuts, and spring plate 454). Each of these components may be made of various materials capable of withstanding an expected environment for the assembly 400 (e.g., atmosphere, vacuum or near-vacuum, underwater, etc.) without failing due to atmospheric pressure, external forces, and/or forces exerted by the springs and other components of the assembly 400. Some or all of the components may also include metallic alloys including one or more metals (e.g., steel, stainless steel, aluminum, nickel, copper, tin, and titanium). Further, some of the components may also use some high-strength plastics, composites, and/or ceramics. Still further, these components may be painted, coated, galvanized, and/or plated to prevent corrosion. Further yet, each of the components may be cast, extruded, machined, and/or forged to give the appropriate shape and strength for their function.

The assembly 400 also includes various high-strength components that are exposed to the propellant while the assembly 400 is in an open configuration (e.g., receptor 426, flashback deflector 402, propellant inlet tube 410, ball bearing 420, ball seat 422, bellows 428, and top cap 404). Each of these components may be also made of various materials capable of withstanding the expected environment for the assembly 400 without failing due to atmospheric pressure, external forces, and/or forces exerted by the springs. Further, the components that are exposed to the propellant need to withstand the expected propellant pressure and flashback forces when the assembly 400 is in an open position during normal operation, during a flashback before the assembly 400 closes, and after the flashback, when the assembly 400 is closed. Still further, the components that are exposed to the propellant need to be made of a material or be coated with a material that does not contaminate the propellant (e.g., a material that resists oxidation when the combustible material includes oxygen). Some or all of the components may also include metallic alloys including one or more metals (e.g., steel, stainless steel, aluminum, nickel, copper, tin, and titanium). Further, some of the components may also use some high-strength plastics, composites, and/or ceramics. Still further, these components may be painted, coated, galvanized, and/or plated to prevent external corrosion and/or internal contamination of the propellant. For example, one or more of the components may include an internal coating when the base material of a particular component is catalytic with the propellant. Further yet, each of the components may be cast, extruded, machined, and/or forged to give the appropriate shape and strength for their function.

Some of the components of assembly 400 have specific construction requirements separate from the components discussed above (e.g., bellows 428, springs, porous media element 430, and burst membrane 408, flashback deflector 402, ball bearing 420, and ball seat 422). The bellows 428 must be sufficiently flexible to deflect with movement of the receptor 426 in relation to the propellant inlet tube 410 while maintaining an effective seal at an interface between the receptor 426 and the propellant inlet tube 410. Further, the bellows 428 must be sufficiently strong to withstand the expected propellant pressure and flashback forces when the assembly 400 is in an open position during normal operation, during a flashback before the assembly 400 closes, and after the flashback, when the assembly 400 is closed. For example, the bellows 428 may include a corrugated layer or multiple corrugated layers of a flexible metallic alloy (e.g., stainless steel, spring steel, and/or an aluminum alloy). In another example, the bellows 428 may include a woven metallic structure with a plastic or rubber interior coating or layer.

The springs may include any metallic and/or plastic material with sufficient rigidly to close the assembly 400 when the burst membrane 408 fails while also having sufficient resilience to maintain closing rigidity after being held in the open position for an extended period of time (e.g., spring steel). The porous media element 430 may be made of various sintered and/or refractory metals and/or ceramics. Further, the porous media element 430 may have various coatings, particularly when the base material of the porous media element 430 is catalytic with the propellant.

The burst membrane 408 must be sufficiently strong to hold the assembly 400 open during normal operation while being capable of fracturing and failing due to thermal and/or pressure energy caused by a flashback. For example, the burst membrane 408 may be made of a rigid plastic. The flashback deflector 402 may also be adapted to conduct thermal energy rapidly from the flashback. As a result, materials chosen for the flashback deflector 402 may have a relatively high thermal conductivity (e.g., various metals). The ball bearing 420, and ball seat 422 may utilize softer materials that are more suitable to provide a seal (e.g., Teflon and TFE fluorocarbons, soft metals (e.g., copper and brass), and composite materials).

FIG. 5 illustrates a cross-sectional view of an example open flashback-arresting deflector and shut-off valve assembly 500, showing propellant flowing through the assembly 500. The assembly 500 provides flashback (i.e., detonation and/or deflagration) protection to propellant (e.g., monopropellant and mixed bipropellant) lines and/or sources upstream from the assembly 500. The propellant enters the assembly 500 via propellant inlet tube 510 as illustrated by arrow 532. The propellant flows around a ball bearing 520 and through one or more apertures (not shown) in a receptor 526, as illustrated by arrows 534. The propellant then flows through a porous media element 530, as illustrated by arrows 535. The porous media element 530 is adapted to permit propellant flow while preventing a flashback from propagating through the porous media element 530. In some implementations, the porous media element 530 is not included.

The propellant continues to flow around the base, up the sides, and over the top of a flashback deflector 502, as illustrated by arrows 536. Further, the flashback deflector 502 may have various channels or apertures to facilitate the flow of propellant around the flashback deflector 502. In some implementations, the flashback deflector 502 is not included. The propellant exits the assembly 500 via propellant outlet aperture 512, as illustrated by arrows 538. In one implementation, compression fittings or other detachable connectors may be attached to the propellant inlet tube 510 and/or propellant outlet aperture 512 so that the assembly 500 may be removeably inserted in the path of propellant from a fluid reservoir such as tanks 226, 228, 230 to a combustion point, such as the injector 238 of FIG. 2. For example, the propellant may travel from the fluid reservoir through a connecting pipe, tube, or other mechanism towards the propellant inlet tube 510, through assembly 500, out propellant outlet aperture 512, and through another connecting pipe, tube, or other mechanism to the combustion point.

Burst member 508 is illustrated intact and adjacent the flashback deflector 502. In one implementation, the burst member 508 has one or more weakened areas where the burst member 508 is intended to fail during a flashback event. The weakened areas are depicted as external and internal circumferential grooves (e.g., groove 562) in the burst member 508. In another implementation, the weakened areas may include a thinner wall near the center of the burst member 508 as compared to a thicker wall near the edges of the burst member 508. Further, the internal circumferential grooves may act as line charges, providing a reservoir of combustible fluid that may be ignited during the flashback event, aiding the failure of the burst member 508 during the flashback event. The burst member 508, in tension, holds the receptor 526 upward against downward force applied by compressed springs (e.g., spring 524). As a result, the ball bearing 520 is held away from a ball seat 522 (or allowed to float freely above the ball seat 522) and the propellant flows relatively unimpeded from the propellant inlet tube 510 to the propellant outlet aperture 512.

FIG. 6 illustrates a cross-sectional view of an example closed flashback-arresting deflector and shut-off valve assembly 600, showing a flashback diverted out of the assembly 600. The assembly 600 provides flashback (i.e., detonation and/or deflagration) protection to propellant (e.g., monopropellant and mixed bipropellant) lines and/or sources upstream from the assembly 600. As depicted in assembly 500 of FIG. 5, the propellant enters the assembly 600 via propellant inlet tube 610 as illustrated by arrow 632. However, in assembly 600, ball bearing 620 is sealed against ball seat 622. As a result, the propellant does not proceed beyond the ball bearing 620.

Springs (e.g., spring 624) cause downward movement of receptor 626 with respect to the propellant inlet tube 610 after fracture and failure of burst member 608. The downward movement of receptor 626 with respect to the propellant inlet tube 610 seals ball bearing 620 against ball seat 622. A flashback event causes the fracture and failure of the burst member 608.

More specifically, the flashback event creates a combustion wave that propagates from the ignition source upstream towards the arrestor in a reverse flow direction as compared to the flow direction of propellant depicted in FIG. 5 (see arrow 638). The combustion wave (i.e., detonation and/or deflagration wave(s)) continues over the top of flashback deflector 602 as illustrated by arrows 636. In some implementations, the flashback deflector 602 absorbs some of the physical/thermal energy of the flashback event.

Regardless, the remaining thermal energy and pressure in the combustion wave causes the burst member 608 to fracture and fail. In some implementations, the flashback deflector 602 includes one or more circumferential grooves (not shown) adjacent the burst member 608. The circumferential grooves form a reservoir of propellant adjacent the burst member 608, which aids in forcing the failure of burst member 608 during the flashback event.

As a result, the failure of burst member 608, the ball bearing 620 seals against the ball seat 622 as discussed above. Further, the failure of burst member 608 causes pressure relief outlets (e.g., shockwave outlet 614) to open, allowing the physical/thermal energy of the flashback event to exit the assembly 600, as illustrated by arrows 635. The pressure relief outlets provide an outlet for exhaust gasses produced by combustion of the propellant as well as some combusted/un-combusted propellant. In some implementations, fragments of burst member 608 after failure are also discharged via the pressure relief outlets. In other implementations, the fragments of burst member 608 after failure remain within the assembly 600. The pressure relief outlets may each incorporate a paper or plastic seal that is broken and/or a plug that is discharged when the exhaust gasses and/or fragments of burst member 608 are discharged from the pressure relief outlets. The paper or plastic seal and/or the plug provides a visual aid that indicates whether a flashback event has occurred.

In one implementation, the assembly 600 is adapted to isolate a detonation wave traveling upstream from an ignition point from reaching a corresponding propellant tank or other upstream propellant feed lines carrying monopropellant or pre-mixed bipropellant. The assembly 600 is spring-loaded and normally held open using the burst element 608. Once the burst element 608 fails, the springs force the assembly 600 to a closed position, thereby isolating upstream propellant from the detonation wave.

FIG. 7 illustrates example operations 700 for arresting a flashback using a flashback-arresting shut-off valve according to the presently disclosed technology. In moving operation 705, propellant (e.g., monopropellant or mixed bipropellant) is moved from a propellant reservoir, through an open flashback-arresting shut-off valve, and to a point of combustion in a normal propellant flow direction. A pump, gravity feed, suction, or other mechanism may effectuate the movement of the propellant. The shut-off valve is positioned in line with the flow of the propellant to the point of combustion so that the shut-off valve may prevent the propellant from flowing from the propellant reservoir to the point of combustion when the shut-off valve is closed.

In experiencing operation 710, the shut-off valve experiences a flashback of the propellant within a propellant line connecting the shut-off valve to the point of combustion in a direction opposite to the normal propellant flow direction. During the flashback, the propellant is ignited within the propellant line, downstream of the shut-off valve, and substantial physical/thermal energy caused by the flashback travels in the direction opposite to the normal propellant flow direction back to the shut-off valve. The flashback may include detonation and/or deflagration.

In fracturing operation 715, a burst member within the shut-off valve fractures and fails. The burst member is intended to fail during a flashback event and is thus constructed of a relatively brittle material (e.g., a rigid plastic or a brittle metal like titanium) that should fail under a detonation impact load. Failure of the burst member causes the releasing and opening operations 720, 725 to occur. In releasing operation 720, compression on a spring-loaded portion of the shut-off valve is released, thereby closing the shut-off valve and sealing the propellant reservoir and propellant lines connecting the shut-off valve to the propellant reservoir from the flashback. In one implementation, after failure of the burst member, which holds the springs in compression, the released compression presses a ball bearing into a seat, which provides the seal.

In opening operation 725, one or more pressure relief outlets that direct the physical/thermal energy and/or un-combusted/combusted propellant out and away from the shut-off valve are opened. The burst member seals the pressure relief outlets from the propellant flowing through the shut-off valve during a normal (or open) operation of the shut-off valve. However, after failure of the burst member, the pressure relief outlets become open to the propellant downstream of the ball bearing and seat. Since the flow path back through the shut-off valve is blocked when the shut-off valve is closed, the physical/thermal energy and/or un-combusted/combusted propellant instead travels out of the shut-off valve via the pressure relief outlets. The pressure relief outlets typically open into a controlled environment, ambient air, and/or a vacuum, in all cases in a location away from the propellant reservoir.

In absorbing operation 730, thermal energy is absorbed by the flashback-arresting shut-off valve to prevent secondary ignition of the propellant within the propellant reservoir and/or propellant lines sealed off from the remainder of the flashback-arresting shut-off valve. The post-combusted gasses within the flashback-arresting shut-off valve likely have a very high temperature, which in turn raises the temperature of the shut-off valve itself. If the temperature of the shut-off valve is allowed to rise high enough, the sealed off propellant source may ignite even though it is not directly exposed to the flashback. To avoid this, the mass of a flashback deflector and/or other components of the flashback-arresting shut-off valve may absorb much of the thermal energy so that the temperature of components of the shut-off valve adjacent the sealed off propellant source does not exceed an auto-ignition point of the propellant.

The above specification, examples, and data provide a complete description of the structure and use of exemplary embodiments of the invention. Since many embodiments of the invention can be made without departing from the spirit and scope of the invention, the invention resides in the claims hereinafter appended. Furthermore, structural features of the different embodiments may be combined in yet another embodiment without departing from the recited claims. 

1. A propellant shut-off assembly for isolating a propellant source, comprising: a burst membrane configured to fail in presence of a flashback; and a biased closed shut-off valve attached to the burst membrane, wherein the shut-off valve is held open by the burst membrane while the burst member is intact.
 2. The propellant shut-off assembly of claim 1, further comprising: a flashback deflector configured to deflect the flashback toward the burst membrane.
 3. The propellant shut-off assembly of claim 1, further comprising: a porous media element configured to permit propellant to flow through the propellant shut-off assembly in a propellant flow direction and prevent the flashback from flowing through the propellant shut-off assembly in a direction opposite the propellant flow direction.
 4. The propellant shut-off assembly of claim 1, wherein the shut-off valve is biased closed using one or more springs storing mechanical energy.
 5. The propellant shut-off assembly of claim 4, further comprising: one or more nuts configured to adjust the closing bias of the one or more springs storing mechanical energy.
 6. The propellant shut-off assembly of claim 1, wherein the shut-off valve includes: a propellant inlet tube with a valve seat at a distal end of the propellant inlet tube; and a receptor with a valve at a distal end of the receptor, wherein the valve is adapted to seal against the valve seat when the propellant shut-off assembly is in a closed position.
 7. The propellant shut-off assembly of claim 6, further comprising: a bellows attached to the propellant inlet tube and the receptor, wherein the bellows provides a seal between the propellant inlet tube and the receptor while allowing the receptor to move in relation to the propellant inlet tube.
 8. The propellant shut-off assembly of claim 1, further comprising: one or more pressure relief outlets configured to provide an outlet for exhaust gasses when the burst membrane fails.
 9. The propellant shut-off assembly of claim 1, wherein the burst member is under tension while intact.
 10. The propellant shut-off assembly of claim 1, wherein the burst member is thinner at its center and thicker at its edges.
 11. The propellant shut-off assembly of claim 1, wherein the burst member includes a plurality of circumferential grooves.
 12. The propellant shut-off assembly of claim 1, wherein propellant is permitted to flow through the propellant shut-off assembly so long as the shut-off valve is held open by the burst membrane and propellant is not permitted to flow through the propellant shut-off assembly when the burst membrane is fractured causing the shut-off valve to close.
 13. The propellant shut-off assembly of claim 1, wherein the flashback includes a detonation wave.
 14. A method of arresting a flashback in a propellant shut-off assembly, the method comprising: experiencing the flashback at the propellant shut-off assembly; fracturing a burst membrane to failure in response to the experiencing operation; closing the propellant shut-off assembly in response to the fracturing operation; and redirecting the flashback out of the propellant shut-off assembly in response to the fracturing operation.
 15. The method of claim 14, further comprising: moving propellant through the propellant shut-off assembly in a propellant flow direction.
 16. The method of claim 14, wherein the flashback occurs downstream of the shut-off assembly and moves in a direction opposite the propellant flow direction back to the propellant shut-off assembly.
 17. The method of claim 14, wherein the closing operation includes: moving a receptor in relation to a propellant inlet tube; and sealing a ball bearing in a ball seat.
 18. The method of claim 14, wherein the flashback includes a detonation wave.
 19. A propellant delivery system comprising: a propellant reservoir; a propellant shut-off assembly for isolating a propellant source, comprising: a burst membrane configured to fail in presence of a flashback; and a biased closed shut-off valve attached to the burst membrane, wherein the shut-off valve is held open by the burst membrane while the burst member is intact; and a propellant injector, wherein the flashback originates between the propellant injector and the propellant shut-off assembly and the propellant shut-off assembly is configured to isolate the propellant reservoir from any components of the propellant delivery system that have failed as a result of the flashback.
 20. The propellant delivery system of claim 19, wherein the propellant shut-off assembly further includes one or more pressure relief outlets configured to provide an outlet for exhaust gasses when the burst membrane fails.
 21. The propellant delivery system of claim 19, wherein the flashback includes a detonation wave. 